Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical Method, Mathematical Method, and PROSPER Software

*Ali Omran Nasar and Shahab D. Mohaghegh*

## **Abstract**

The production of any oil reservoir is a result of the natural forces around the reservoir. These forces are called driving mechanism, which stars strong in the early well life, and then becomes weak to deliver fluids from the wellbore into the surface. Here, an artificial lift method should be ready to be signed directly in order to continue producing fluids. There are several types of artificial lift methods used in the petroleum industry such as Gas Lift. In this chapter, an oil well under a continuous gas lift process located in the Amal oil field is analyzed using three different methods. These methods are graphical method, mathematical method, and PROSPER software. The aim of this chapter is to determine the gas injection point and valve distribution of the gas lift system correctly. From the well history, the well had been put under a gas lift process with the inaccurate design of the gas injection point and valve distribution that result in a high water cut. In the end of this chapter, the steps of redesigning of the gas lift process by using the three mentioned methods showed great results that will be discussed in more details.

**Keywords:** artificial lift, gas lift, design methods (graphical, mathematical, prosper), low water cut, high productivity

## **1. Introduction**

Most oil wells will flow naturally for some period of time after they begin producing. This period of time might take several months to several years depending on the pressure supported. The reservoir pressure provides enough energy to bring fluid to the surface in a flowing well. As the well produces this energy is consumed and at some point, there is no longer enough energy available to bring the fluid to the surface, and the well will be put under one of artificial lift methods. The commonly used artificial lift methods in the petroleum industry are Sucker Rod Pumping, Hydraulic Pumping, Electrical Submersible Pumping, Gas Lift, Plunger Lift, and

**Figure 1.** *Artificial lift systems [1].*

**Figure 2.**

*Percentage of usage of artificial lift in the world for around 900,000 wells [1].*

Progressing Cavity Pumping. Each one of the mentioned methods that are shown in **Figure 1** has its own explanations, this chapter will only cover the gas lift.

Moreover, approximately 50% of wells worldwide need artificial lift systems. There are varieties in the using methods depending on some factors. The pie chart in **Figure 2** shows the estimated worldwide usage of different lift methods in recent years.

## **2. Gas lift systems**

Gas Lift is one of the artificial lift methods that is widely used in oil wells. This method utilizes an external source of high-pressure gas for supplementing formation *Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*

**Figure 3.** *Basic components for a gas lift system [1].*

gas to reduce the bottom-hole pressure and lift the well fluids. Usually in the gas lift process, there is plenty of gas available in the area. The basic component of gas lift consists of gas compression which is composed of a compressor and dehydration plant, manifolds, gas lines, meters, and rate control devices [1]. The surface and subsurface components of the gas lift system are shown in **Figure 3**.

## **3. Types of gas lift supplements**

There are two basic types of gas lift supplements. They are called continuous-flow gas lift and intermittent gas lift. The principle of the two types is described as: Gas lifting fluids from a well by the continuous injection of high-pressure gas to supplement the reservoir energy (continuous flow), or by injecting gas beneath an accumulated liquid slug for a short time to move the slug to the surface (intermittent lift) [2]. In this chapter, the well had been put under a continuous gas lift since there is plenty of gas available in the Amal oil field.

## **4. Gas lift valves**

Continuous gas lift usually consists of a number of unloading valves with an orifice valve at the operating point. The role of the unloading gas lift valve is to allow smooth, positive, and reliable unloading of the well to the orifice over many years with continuously changing conditions. There are different types of unloading valves, namely casing pressure-operated valve (usually called a pressure valve), throttling pressure valve (also called a proportional valve or continuous flow valve),

fluid-operated valve (also called a fluid valve), and combination valve (also called a fluid open-pressure closed valve). Different gas lift design methods have been developed and used in the oil industry for applications of these valves [3]. The selection of the gas lift valve depends on the gas injection and well condition. Moreover, the valve spacing is not only the distance between the valves but a range where API recommends to meet the following desired [3]:


## **5. Design methods**

Three methods have been used in this chapter to detect the gas injection point and valve locations. These methods are: the graphical method, mathematical method, and PROSPER software. Each method has a different technique to detect the gas injection but they are same in the principle. The procedure of all the mentioned methods will be explained in the coming subtitle of this chapter.

## **5.1 Graphical method**

This method depends on some data to draw a flow chart as shown in **Figure 4**. It is an old method and needs the best fit of drawing to have accurate results of gas injection

**Figure 4.** *Example of the procedure of the graphical method [4].*

*Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*

point and valve location. The needed data are: well head pressure, bottom hole pressure, reservoir pressure, kick off pressure, operating pressure, static gradient pressure, unloading gradient pressure, kick off gradient pressure, oil flow rate, water flow rate, average specific gravity (oil specific gravity, water specific gravity), and total depth. The steps will be explained in the calculations and results section of this chapter.

#### **5.2 Mathematical method**

This method depends on calculations and does not need any drawing to detect the gas injection and valve locations. All the calculations will be done by using the below equations. However, it depends on some data that are taken from the graphical method or might be available from the well information such as static gradient and unloading gradient. The equations used in the mathematical methods to determine the gas injection point and the valve locations are listed below [5]:

$$\mathbf{T} = \frac{\mathbf{100F}^o + \left[\mathbf{70} + \frac{\mathbf{1.6^\circ \text{Depth}}}{100}\right]}{2} \tag{1}$$

$$\gamma\_{\text{avg}} = \left[ \left( \gamma\_o \stackrel{\text{oil rate}}{\text{total rate}} \right) + \left( \gamma\_{\text{w}} \stackrel{\text{water rate}}{\text{total rate}} \right) \right] \tag{2}$$

$$\text{Gs} = \text{y}\_{\text{avg}}\,^\*\mathbf{0}.433\tag{3}$$

$$\text{Dv1} = \frac{\mathbf{P\_{so}} - \mathbf{P\_{wh}}}{\mathbf{G\_s}} \tag{4}$$

$$\mathbf{Dv2} = \mathbf{Dv1} + \left[\frac{\mathbf{P\_{so}} - \mathbf{P\_{wh}} - (\mathbf{Dv1} \ast \mathbf{G\_u})}{\mathbf{G\_s}}\right] \tag{5}$$

From Eq. (5), engineers can continue deriving equations to calculate the next valve locations until reaching the gas injection point or depth of the static oil level.

#### **5.3 PROSPER**

PROSPER is a well performance, design, and optimization program that is part of the Integrated Production Modeling Toolkit (IPM). It is a tool that is introduced by the industry to be used for the artificial lift application. This software provides more flexibility and accurate results for production engineering just needs more data to be inserted in it. **Figure 5** shows the opened window of PROSPER software.

## **6. Case study**

The case that has been studied in this chapter is an oil well in the Amal field which belongs to Harouge Oil Company. The well that chosen is located in the N area, and named as X. The N area is located northeastern part of Amal Field, which encloses an area of 48,000 acres. The average reservoir pressure is maintained at around 3180 psia by an active edge-bottom water drive. **Figure 6** shows the location of Amal wells [6].

**Figure 5.** *PROSPER software first page.*

**Figure 6.** *Amal field well location map [6].*

## **6.1 Field data for N\_Area**

The field data from the N area have been brought for analysis in this study. The data that need to be used for gas lift optimization are listed in **Table 1**. These data are arranged separately based on the PROSPER simulator input requirement, since the software needs more data, and also for other methods. **Tables 1**–**5** show the obtained data from Harouge Oil Company will give a better that will be used in this study.

## **7. Calculations and results**

The three mentioned methods will be applied for well X to detect gas injection point and valve distributions respectively. Short Expansions of each method will be shown in the coming sections of this chapter.

*Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*

## **7.1 Graphical method results**

In this method, there are some steps that need to be followed in order to draw a flow chart such as in **Figure 4**. These steps are: First, calculate the average specific gravity by using Eq. (3), second, plot Pwh Pso at zero depth as shown in **Figure 7**, after plotting Pwh and Pso, calculate Pso equivalent to total depth with plus 100 Psia and minus 100 Psia as a safety factor and plot them at the total depth. Third, plot Pwf at total depth in order to determine the flowing level, then choose any depth to calculate


#### **Table 1.**

*PVT \$ IPR data for well (X) [6].*


#### **Table 2.**

*Trajectory description data for well (X) [6].*


#### **Table 3.**

*Include the casing information tubing information, and pressures for well (X) [6].*


#### **Table 4.**

*Include the reservoir temperature, bottom hole temperature well head temperature and production test for well (X) [6].*


**Table 5.**

*Include the productivity index (J) and kill fluid properties for well (X) [6].*

Pwf equivalent at that depth. After having all this information, the gas injection point can be detected and the first valve location is also determined. Finally by using the ruler (rule of thumb) other valve locations can be determined easily. From **Figure 7** the valve location are determined and listed in **Table 6**.

## **7.2 Mathematical method results**

In this method, only calculation will be done to determine the valve locations and compare them with the graphical method, the gas injection point cannot be detected from this method. The last valve location will be the gas injection point. The procedures of the mathematical method for well X are: First, the static gradient has been calculated in the graphical method which is 0.367, while the unloading gradient needs to be estimated, which is the slope of the line that is used to detect gas injection point

**Figure 7.** *Design by hand of gas lift for well X.*

*Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*


#### **Table 6.**

*Shows valve locations for well X by using a graphical method.*

in **Figure 7** which is 0.141 Psia/ft. Second, after having the unloading and static gradient first valve location can be estimated by using Eq. (4) which is 2785 ft. Third, from now on all the coming valve locations can be easily estimated by using Eq. (5). For further valve locations, equations can be generated just one point should be taken into production engineering consideration, which is the space between valves that is not less than 200 ft. and does not pass the gas injection point as well. The results of the mathematical method are listed in **Table 7**.

#### **7.3 PROSPER software results**

The PROSPER software is used in this study to get better optimization of the gas lift design and to compare its results with other methods. All the needed data are listed in **Tables 1**–**5**. The coming software windows show input data with their matching and the valves location (**Figures 8**–**12**).

#### **7.4 Result's comparison**

The results of the gas lift process using the graphical method, mathematic method, and PROSPER Software are listed in the **Table 8**. The result shows a difference in the values between the mathematical method and the graphical method both results are acceptable as long as the distance between two valves is more than 200 ft. The mathematical methods resulted more valves than graphical method. The PROSPER Software results are closer to the graphical method than the mathematic method, which indicates that software might be more accurate in scaling drawing than hand.


**Table 7.**

*Valves locations for well X by using mathematical method.*


*Gas lift design mean menu and well information.*


**Figure 9.**

*Gas lift design rate with valve calculations, PROSPER software result.*

### **7.5 Casing and tubing pressures**

After having all the gas injection points and the depth of valves by the used methods, the calculation of pressure in casing and tubing at each valve depth for well X can be done by using the following equation [4]:

*Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*

#### **Figure 10.**

*Valve calculations with tubing, opening, and closing pressure.*


**Figure 11.** *Gas lift design report results.*

**Figure 12.** *Complete result of gas lift design for well X.*


#### **Table 8.**

*Comparison between the graphical method, mathematical method, and PROSPER.*


**Figure 13.** *Weight of gas column [4].*

*Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*


#### **Table 9.**

*Casing and tubing pressure for each valve location of graphical method for well X.*

## **8. Conclusions**


## **Acknowledgements**

The authors would like to express their gratitude to the Harouge Oil Company for supplying the data used in this chapter, and also for providing the software that was used in the study.

## **Nomenclature**



## **Author details**

Ali Omran Nasar<sup>1</sup> \* and Shahab D. Mohaghegh<sup>2</sup>

1 Faculty of Engineering, Petroleum Engineering Department, Sirte University, Sirte, Libya

2 Petroleum and Natural Gas Engineering Department, West Virginia University, USA

\*Address all correspondence to: ali\_omran95@yahoo.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Optimizations of an Oil Well in Amal Field under a Continuous Gas Lift by Using Graphical… DOI: http://dx.doi.org/10.5772/intechopen.112988*

## **References**

[1] Schlumberger Gas Lift Design and Technology Well Completions and Productivity Chevron Main Pass 313 Optimization Project. USA. 2000

[2] Brown KE et al. The Technology of Artificial Lift Methods. Vol. 2a. Tulsa, Oklahoma: PennWell Company; 1980

[3] Guo B. Petroleum Production Engineering a Computer Assistant. USA: University of Louisiana at Lafayette, Elsevier Science & Technology Books; Feb 2007

[4] Abdelstar, Elsqer2003-2004. Class Note of Production Engineering II. Sirte University Fall; 2003/2004

[5] API Gas Lift Manual Subsurface Survey, Book 6 of the Vocational Training Series. 3rd ed. 1994

[6] Harouge Oil Company, Amal field, N\_location, monthly reports. 2018/2019
